Interpretive Summary: During pregnancy, the fetus obtains energy by using glucose (sugar) supplied by its mother. The mother meets the increased needs of the fetus mainly by increasing the production of glucose by the liver. Adolescent girls may be unable to meet the demands of their own growth in addition to the demands of the developing fetus. In this study, we measured the production of glucose, both by the liver and by breakdown of stored glucose, in pregnant adult women and adolescent girls in the first and third trimesters of pregnancy. We found that glucose production increased as pregnancy progressed in both adult women and adolescent girls, although the amount of the increase in the adolescents was less than that of the adult women. The results of this study suggest that adolescent girls and adult women meet the fetus' need for energy differently.

Technical Abstract:
Fetal energy demands are met mostly from oxidation of maternally supplied glucose. In pregnant adults this increased glucose requirement is met by an increase in gluconeogenesis. It is not known, however, whether, like their adult counterparts, pregnant adolescent girls can increase gluconeogenesis and, hence, glucose production. Our objective was to measure glucose kinetics in 8 pregnant adolescents and 8 adult women. We measured glucose kinetics after an overnight fast by using a primed-constant 6-h U-(13)C-glucose infusion at the end of trimester 1 and early trimester 3. From trimester 1 to trimester 3, whole-body glucose production increased significantly in both groups (P < 0.01). However, whereas the weight-specific rate in adults increased by 18.2%, it increased by only 14.3% in adolescents. In adults, the increase in whole-body glucose production was largely due to a significant increase (P < 0.01) in the rate of gluconeogenesis, but in adolescents there was no change in whole-body gluconeogenesis, and weight-specific gluconeogenesis actually decreased by 11.7%. In both groups, the rate of whole-body glycogenolysis increased significantly (P < 0.05) in trimester 3, and in adolescents it increased by 95%. These findings suggest that, in the fasted state in late pregnancy, pregnant adolescents cannot increase weight-specific glucose production by the same magnitude as their adult counterparts. Furthermore, whereas adult women increase glucose production primarily through gluconeogenesis, adolescents do so through glycogenolysis.